soil 16s rDNA
a secondary PCR was performed by using the 16S rRNA V3-V4 region PCR amplicon and Nextera XT Index Kit with dual indices and Illumina sequencing adapters (Illumina). The indexed PCR product quality was assessed on the Qubit 4.0 Fluorometer (Thermo Scientific) and Qsep100TM system. Equal amount of the indexed PCR product was mixed to generate the sequencing library. At last, library was sequenced on an Illumina MiSeq platform and paired 300 bp reads were generated.